Field of the Invention
The invention concerns techniques for magnetic resonance angiographic imaging or magnetic resonance perfusion imaging. In particular, the invention concerns magnetic resonance angiographic imaging with ultrashort echo times.
Description of the Prior Art
Various techniques are known for imaging blood vessels by means of magnetic resonance (MR) imaging (MR angiographic imaging). In one family of techniques, known as spin labeling methods, typically a scan sequence is carried out in which nuclear spins are prepared magnetically in a preparation region. Due to blood flow, the prepared nuclear spins in the blood move as a function of time into the scan region. Therein, image data of the prepared nuclear spins are acquired. A resultant image is typically obtained through a combination of the image data with reference image data. In this regard, the reference image data also map the scan region, although the nuclear spins are differently prepared than in the case of the image data. By this means, it is possible for blood vessels to be imaged with a comparatively high contrast in relation to the background, which is imaged the same or almost the same in the image data and the reference image data.
However, such conventional techniques of MR angiographic imaging can have various disadvantages. For instance, it can often occur that the scan sequences that are used produce a relatively high noise level in the interior of the MR scanner. Depending on the type of MR scanner and the type of scan sequence, the noise levels can reach a value of 100 dB(A). In such a case, it may be necessary for the person under examination to wear ear protection.
In order to lessen the noise level, various sequence optimizing techniques are known (see e.g. DE 10 2014 205 888.0). By means of such techniques, it is possible for the noise level to be reduced significantly. In particular, it is possible for the noise level to be reduced such that ear protection is unnecessary.
However, scan sequences are known that profit to only a small extent from such sequence optimization techniques. These are, in particular, scan sequences that are dependent on relatively rapid gradient pulses and relatively short switchover times of the gradient pulses in order to implement the required time sequence. In such cases, a noise reduction is often possible with adaptation of various parameters of the scan sequence, for example, a spatial resolution of the acquired MR data, echo time TE, repetition time TR, etc. However, such an adaptation of the parameters of the scan sequence can have a negative influence on the quality of the resultant image. The parameter space within which the parameters of the scan sequence can be adapted can also be technologically and/or physically restricted.
Particularly for scan sequences for MR angiographic imaging, a reduction in the noise level by means of the techniques mentioned above for sequence optimization is not possible or is possible only to a limited extent. This is because techniques of MR angiographic imaging are often based on rapid gradient echo-based scan sequences.
There is therefore a need for improved MR angiographic imaging techniques. There is a need, in particular, for techniques which provide a relatively quiet scan sequence for MR angiographic imaging. There is also a need, in particular, for such techniques which enable a relatively high quality in a resultant image of the MR angiographic imaging.